The first income tax was assessed in 1862 to raise funds for the American Civil War, with a rate of 3%. Today the IRS collects over $2.4 trillion each tax year. It processes around 234 million tax returns annually.

The Revenue Act of 1862 was passed as an emergency and temporary war-time tax. It copied a relatively new British system of income taxation, instead of trade and property taxation. The first income tax was passed in 1862:

The initial rate was 3% on income over $800, which exempted most wage-earners.

In 1862 the rate was 3% on income between $600 and $10,000, and 5% on income over $10,000.

In 1864 the rate was 5% on income between $600 and $5,000; 7.5% on income $5,000–10,000; and 10% on income $10,000 and above.

By the end of the war, 10% of Union households had paid some form of income tax, and the Union raised 21% of its war revenue through income taxes.[3]

After the Civil War, Reconstruction, railroads, and transforming the North and South war machines towards peacetime required public funding. However, in 1872, seven years after the war, lawmakers allowed the temporary Civil War income tax to expire.

The Congress shall have power to lay and collect taxes on incomes, from whatever source derived, without apportionment among the several States, and without regard to any census or enumeration.

”

This granted Congress the specific power to impose an income tax without regard to apportionment among the states by population. By February 1913, 36 states had ratified the change to the Constitution. It was further ratified by six more states by March. Of the 48 states at the time, 42 ratified it. Connecticut, Rhode Island, and Utah rejected the amendment; Pennsylvania, Virginia, and Florida did not take up the issue.[5]

A copy of the very first IRS 1040 form, dated 1913, can be found at the IRS website[6] showing that only those with incomes of $3,000 (adjusted for inflation, the equivalent of $68,612 in 2011) or more were instructed to file.

People filing tax forms in 1920.

In the first year after ratification of the Sixteenth Amendment, no taxes were collected—instead, taxpayers simply completed the form and the IRS checked it for accuracy. The IRS's workload jumped by ten-fold, triggering a massive restructuring. Professional tax collectors began to replace a system of "patronage" appointments. The IRS doubled its staff, but was still processing 1917 returns in 1919.[7]

From the 1950s through the 1970s, the IRS began using technology such as microfilm to keep and organize records. Access to this information proved controversial, when President Richard Nixon's tax returns were leaked to the public. His tax advisor, Edward L. Morgan, became the fourth law-enforcement official to be charged with a crime during Watergate.[8]

John Requard. Jr., accused of leaking the documents, collected delinquent taxes in the slums of Washington. In his words:

We went after people for nickels and dimes, many of them poor and in many cases illiterate people who didn't know how to deal with a government agency.

He admits he saw the returns, but denies he leaked them. When asked if he would have leaked the documents, he said: "I probably would have said, 'Yes, I'm in.'"[9]

Reporter Jack White of The Providence Journal, won the Pulitzer Prize for reporting about Nixon's tax returns. Nixon, with a salary of $200,000, paid $792.81 in federal income tax in 1970 and $878.03 in 1971, with deductions of $571,000 for donating "vice-presidential papers".[10] This was one of the reasons for his famous statement: "Well, I'm not a crook. I've earned everything I've got."

So controversial was this leak, that most later US Presidents released their tax returns (though sometimes only partially). These returns can be found online at the Tax History Project.[11]

By the end of the Second World War, the IRS was handling sixty million tax returns each year, using a combination of mechanical desk calculators, accounting machines and pencil and paper forms. In 1948 punch card equipment was used. The first trial of a computer system for income tax processing was in 1955, when an IBM 650 installed at Kansas City processed 1.1 million returns. The IRS was authorized to proceed with computerization in 1959, and purchased IBM 1401 and IBM 7070 systems for local and regional data processing centers. The Social Security Number was used for taxpayer identification starting in 1965. By 1967, all returns were processed by computer and punched card data entry was phased out.[12]

Information processing in the IRS systems of the late 1960s was in batch mode; microfilm records were updated weekly and distributed to regional centers for handling tax inquiries. A project to implement an interactive, realtime system, the "Tax Administration System" was launched, that would provide thousands of local interactive terminals at IRS offices. However, the General Accounting Office prepared a report critical of the lack of protection of privacy in TAS, and the project was abandoned in 1978.[12]

In 1995, the IRS began to use the public Internet for electronic filing. Since the introduction of e-filing, self-paced online tax services have flourished, augmenting the work of tax accountants, who were sometimes replaced.

In 2003, the IRS struck a deal with tax software vendors: The IRS would not develop online filing software and, in return, software vendors would provide free e-filing to most Americans.[13] In 2009, 70% of filers qualified for free electronic filing of federal returns.[14]

According to an inspector general's report, released in November 2013, identity theft in the United States is blamed for US$4 billion worth of fraudulent 2012 tax refunds by the IRS. Fraudulent claims were made with the use of stolen taxpayer identification and Social Security numbers, with returns sent to addresses both in the US and internationally. Following the release of the findings, the IRS stated that it resolved most of the identity theft cases of 2013 within 120 days, while the average time to resolve cases from the 2011/2012 tax period was 312 days.[15] In January 2015 Fox News obtained an email which predicted a messy tax season on several fronts. The email was sent by IRS Commissioner Koskinen to workers.[16]

In September 2014, IRS Commissioner John Koskinen expressed concern over the organization's ability to handle Obamacare and administer premium tax credits that help people pay for health plans from the health law’s insurance exchanges. It will also enforce the law’s individual mandate, which requires most Americans to hold health insurance.[17] In January 2015 Fox News obtained an email which predicted a messy tax season on several fronts. The email was sent by IRS Commissioner Koskinen to workers. Koskinen predicted the IRS will shut down operations for two days later this year which will result in unpaid furloughs for employees and service cuts for taxpayers. Koskinen also said delays to IT investments of more than $200 million may delay new taxpayer protections against identity theft.[16] In January 2015 the editorial board of the NYtimes called the IRS budget cuts penny-wise-and-pound-foolish, where for every dollar of cuts in the budget, $6 were lost in tax revenue.[18]

As early as the year 1918, the Bureau of Internal Revenue began using the name "Internal Revenue Service" on at least one tax form.[19] In 1953, the name change to the "Internal Revenue Service" was formalized in Treasury Decision 6038.[20]

As a result of that Act, the IRS now functions under four major operating divisions: Large Business and International division (LB&I), the Small Business/Self-Employed (SB/SE) division, the Wage and Investment (W&I) division, and Tax Exempt & Government Entities (TE/GE) division. Effective October 1, 2010, the name of the Large and Mid-Size Business division changed to the Large Business & International (LB&I) division.[23] The IRS also includes a criminal law enforcement division (IRS Criminal Investigation Division). While there is some evidence that customer service has improved, lost tax revenues in 2001 were over $323 billion.[24]

The IRS has its headquarters in Washington, D.C., and does most of its computer programming in Maryland. It currently operates ten service centers around the country (in Andover, MA; Holtsville, NY; Philadelphia, PA; Atlanta, GA; Memphis, TN; Austin, TX; Cincinnati, OH; Fresno, CA; Kansas City, MO; and Ogden, UT), at which returns sent by mail are received. These centers do the actual tax processing; different types of returns are processed at the various centers (with some centers processing individual returns and others processing business returns). The IRS also operates three computer centers around the country (in Detroit, Michigan; Martinsburg, West Virginia; and Memphis, Tennessee).[25]

There have been 47 previous commissioners of Internal Revenue and 26 acting commissioners since the agency was created in 1862.[26]

Senior official at the Office of Management and Budget Daniel Werfel was announced as the acting Commissioner of Internal Revenue.[27] Werfel, who attended law school at the University of North Carolina and attained a master's degree from Duke University, prepared the government for a potential shutdown in 2011 by determining which services that would remain in existence.[27][28]

No IRS commissioner has served more than five years and one month since Guy Helvering, who served 10 years until 1943.[29] The most recent commissioner to serve the longest term was Doug Shulman, who was appointed by President George W. Bush and served for five years.[29]

Volunteer Income Tax Assistance (VITA) and Tax Counseling for the Elderly (TCE) are volunteer programs that the IRS runs to train volunteers and provide tax assistance and counseling to taxpayers.[31] Volunteers can study e-course material, take tests, and practice using tax-preparation software. Link & Learn Taxes (searchable by keyword on irs website), is the free e-learning portion of VITA/TCE program for training volunteers.

For fiscal year 2009, the U.S. Congress appropriated spending of approximately $12.624 billion of "discretionary budget authority" to operate the Department of the Treasury, of which $11.522 billion was allocated to the IRS. The projected estimate of the budget for the IRS for fiscal year 2011 was $12.633 billion.[34] By contrast, during Fiscal Year (FY) 2006, the IRS collected more than $2.2 trillion in tax (net of refunds), about 44 percent of which was attributable to the individual income tax. This is partially due to the nature of the individual income tax category, containing taxes collected from working class, small business, self-employed, and capital gains. The top 5% of income earners pay 38.284% of the federal tax collected.[35][36]

As of 2007, the agency estimates that the United States Treasury is owed $354 billion more than the amount the IRS collects.[37]

In 2011, 234 million tax returns were filed allowing the IRS to collect $2.4 trillion out of which $384 billion were attributed to mistake or fraud.[38]

In September 2006, the IRS started to outsource the collection of taxpayers debts to private debt collection agencies. Opponents to this change note that the IRS will be handing over personal information to these debt collection agencies, who are being paid between 29% and 39% of the amount collected. Opponents are also worried about the agencies' being paid on percent collected, because it will encourage the collectors to use pressure tactics to collect the maximum amount. IRS spokesman Terry Lemons responds to these critics saying the new system "is a sound, balanced program that respects taxpayers' rights and taxpayer privacy." Other state and local agencies also use private collection agencies.[39]

In March 2009, the IRS announced that it would no longer outsource the collection of taxpayers debts to private debt collection agencies. The IRS decided not to renew contracts to private debt collection agencies, and began a hiring program at its call sites and processing centers across the country to bring on more personnel to process collections internally from taxpayers.[40] As of October 2009, the IRS has ceased using private debt collection agencies.

In September 2009, after undercover exposé videos of questionable activities by staff of one of the IRS's volunteer tax-assistance organizations were made public, the IRS removed ACORN from its volunteer tax-assistance program.[41]

The IRS publishes tax forms which taxpayers are required to choose from and use for calculating and reporting their federal tax obligations. The IRS also publishes a number of forms for its own internal operations, such as Forms 3471 and 4228 (which are used during the initial processing of income tax returns).

In addition to collection of revenue and pursuing tax cheaters, the IRS issues administrative rulings such as revenue rulings and private letter rulings. In addition, the Service publishes the Internal Revenue Bulletin containing the various IRS pronouncements.[42] The controlling authority of regulations and revenue rulings allows taxpayers to rely on them. A private letter ruling is good for the taxpayer to whom it is issued, and gives some explanation of the Service's position on a particular tax issue.[43] Additionally, a private letter ruling reasonably relied upon by a taxpayer allows for the waiver of penalties for underpayment of tax.

As is the case with all administrative pronouncements, taxpayers sometimes litigate the validity of the pronouncements, and courts sometimes determine a particular rule to be invalid where the agency has exceeded its grant of authority. The IRS also issues formal pronouncements called Revenue Procedures, that among other things tell taxpayers how to correct prior tax errors. The IRS's own internal operations manual is the Internal Revenue Manual, which describes the clerical procedures for processing and auditing tax returns in excruciating detail. For example, the Internal Revenue Manual contains a special procedure for processing the tax returns of the President and Vice President of the United States.[43]

More formal rulemaking to give the Service's interpretation of a statute, or when the statute itself directs that the Secretary of the Treasury shall provide, IRS undergoes the formal regulation process with a Notice of proposed rulemaking (NPRM) published in the Federal Register announcing the proposed regulation, the date of the in-person hearing, and the process for interested parties to have their views heard either in person at the hearing in Washington, D.C., or by mail. Following the statutory period provided in the Administrative Procedure Act the Service decides on the final regulations "as is," or as reflecting changes, or sometimes withdraws the proposed regulations. Generally, taxpayers may rely on proposed regulations until final regulations become effective. For example, human resource professionals are relying on the October 4, 2005 Proposed Regulations[44] (citation 70 F.R. 57930-57984)[45] for the Section 409A on deferred compensation (the so-called Enron rules on deferred compensation to add teeth to the old rules) because regulations have not been finalized.

The IRS has on more than one occasion been accused of abusive behavior.[46][47][48][49] Testimony was given before a Senate subcommittee that focused on cases of overly aggressive IRS collection tactics in considering a need for legislation to give taxpayers greater protection in disputes with the agency.

Congress passed the Taxpayer Bill of Rights III on July 22, 1998, which shifted the burden of proof from the taxpayer to the IRS in certain limited situations. The IRS retains the legal authority to enforce liens and seize assets without obtaining judgment in court.[50]

Michael Minns was the defense lawyer in a case against the IRS on behalf of James and Pamela Moran, after an initial indictment in what Minns asserts was an IRS smear campaign that virtually canvassed the taxpayers' own hometown and surrounding area.[51] The original indictment was associated with the Morans' involvement with a tax shelter provider, Anderson's Ark & Associates. The Morans were eventually acquitted in the case.[52]

Minns also had previously asserted that the behavior of two IRS attorneys at law, Kenneth McWade and William A. Sims, constituted legal misconduct and recommended them for disbarment. Following an investigation, the law licenses of the IRS attorneys were duly suspended for a two-year period after a federal court ruling found that the two had indeed defrauded the courts in connection with 1,300 tax shelter cases. In 2003, the United States Court of Appeals for the Ninth Circuit concluded that the IRS lawyers had corruptly agreed with certain taxpayers that no tax collection actions would be taken against them—in return for testimony against other taxpayers. The court also asked why the IRS had not punished the two.[53]

In 2013, the IRS became embroiled in a political scandal in which it was discovered that the agency subjected conservative or conservative-sounding groups filing for tax-exempt status to extra scrutiny.[54]

On September 5, 16 months after the scandal first erupted, a Senate Subcommittee released a report that confirmed that Internal Revenue Service used inappropriate criteria to target Tea Party groups, but found no evidence of political bias.[55] The chairman of the Senate Permanent Subcommittee on Investigations confirmed that while the actions were "inappropriate, intrusive, and burdensome," the Democrats have often experienced similar treatment.[56] Republicans noted that 83% of the groups being held up by the IRS were right-leaning; and the Subcommittee Minority staff, which did not join the Majority staff report, filed a dissenting report entitled, “IRS Targeting Tea Party Groups.” [57]

On May 25, 2015, the agency announced that criminals had illegally accessed the private tax information of over 100,000 taxpayers over a period of several months. By providing Social Security Numbers and other information obtained from prior computer crimes, the criminals were able to use the IRS's online "Get Transcript" function to have the IRS provide them with the tax returns and other private information of American tax filers.[58]

^Form 1040, Individual Income Tax Return for year 1918, as republished in historical documents section of Publication 1796 (Rev. February 2007), Internal Revenue Service, U.S. Department of the Treasury. Form 1040s for years 1918, 1919, and 1920 bore the name "Internal Revenue Service". For the 1921 tax year, the name was dropped, then was re-added for the 1929 tax year.

^See Table, p. 115, Budget of the U.S. Government: Fiscal Year 2011, Office of Management and Budget, Executive Office of the President of the United States (U.S. Gov't Printing Office, Washington, 2010), at Whitehouse.gov (PDF)